Sound signal apparatus



J. R. MaCKAY SOUND SIGNAL `APPARATUS Feb. 1, 1944.

,Original Filed March 14. 1938 2 Sheets-Sheet 1 Feb. 1, 1944. J, R,MaCKAY l2,340,604'

SOUND SIGNAL APPARATUS Original Filed March 14, 1938 2 Sheets-Shaq?. 2

Patented Feb. 1', 1944 i SOUND lSIGNAL APPARATUS John R. MacKay, WestCaldwell, N. J., assignor to Wallace & Tiernan Products, Inc.,Belleville, N. J., a corporation of New Jersey Original applicationMarch 14, 1938, Serial No. 195,893. Divided and this application April11, 1940, Serial No. 329,059

6 Claims.

This invention relates to sound signal apparatus, and more particularlyto signalling or alarm devices of electrically operated type, such ashorns, and to control means for signalling apparatus of the characterstated. The present application is a division of my -co-pendingapplication Serial No. 195,893, led March 14, 1938, for Sound signalapparatus, now Patent No. 2,306,819, granted December 29, 1942. Anespecially advantageous use or embodiment of the invention is in foghorns, wherein'ruggedness, power of sound, and dependability overlongperiods of time are important criteria. Such horns are often used onfloating buoys, and the requirements of a satisfactory horn for such useare particularly severe. All parts must be of a type suitable for use onbuoys, where they will be subject to continuous operation, exposure tothe elements and to frequent submergence, and to operation at all anglesdue to the swinging and listing of the buoy. As buoys are frequentlycollided with, all parts -of the horn and program mechanism must be ofsuch construction that they will not be vdamaged -or operation affectedby any jar or bump which the buoy may receive, other than one where thehorn or mechanism is actually hit and damaged in consequence. It is acommon requirement of horns so used, that they must sound from two tofour blasts of about one second per minute, and that this operation iscontinuous for 24 hours per day for each day of the year.

In general, sound signals such as fog horns have comprised anelectromagnet, an armature, a diaphragm associated with the armature,and make-and-break contacts operated, buzzer fashion, by the armature.Certain difliculties, however, have been found with devices heretoforeknown or available. For example, the pitch of the horn depends on thestiffness of the diaphragmY and inversely on the weight of the armature;and attempts to obtain a pitch high enough for -good carrying qualityhave either required a sacrifice of power or involved a tendency tobreak on the part `of the relatively stii diaphragm used,

when flexed with suincient amplitude to create a powerful signal.Furthermore, although it is usually desirable to space .the diaphragmrelatively far away from the armature, with a connecting member, it hasbeen found that the spring then employed to support the end of thearmature distantfrom the diaphragm, is very apt to break upon continuedvibration of otherwise desirable power.

The present invention is particularly designed to remedy one or more ofthese and other difficulties inherent in prior art devices, and afurther object of the invention is to provide apparatus of the characterdescribed having satisfactory power and pitch characteristics, which isat the same time highly reliable and adapted for operation overextremely long periods of time Without even partial failure orappreciable reduction in its output due to wear. Another object is toprovide more satisfactory contact structures in sound signals, andlikewise eflicient arrangements for preventing or greatly reducing Wearof the contacts.

A still further and notably important object is tov provide an improvedstructure in sound signal devices whereby the amplitude of vibration maybe accurately adjusted or set, and a like important object is theprovision of novel means for maintaining a constant yamplitude ofvibration over long periods of operation.

Other objects are to provide, relative to fog horns and like signalapparatus; an improved and long-Wearing diaphragm structure; a simplerand more efiicient assembly of vibrating parts; and generally sturdierand more reliable arrangement of loperating and control elements.

Other objects' and advantages include those which are hereinafter statedor apparent, or which are incidental to the invention. The nature of thelatter will be conveniently explained by reference to the followingdescription and accompanying drawings, which set forth, by Way ofexample, certain presently preferred embodiments of the invention.

In the drawings:

Fig. 1 is an elevation yof a complete fog h-orn and control unitembodying the invention;

' Fig. 2 is an enlarged longitudinal section of the horn and itsoperating parts;

Fig. 3 is an elevation of the upper end of Fig.2;

Fig. 4 is a section on line 4-4 of Fig. 2; and

Fig. 5 is a general wiring diagram.

As generally shown in Fig. l, the sound signal device and its associatedcontrol instrumentalities may be conveniently combined in a single unit,comprising an open-mouthed trumpet or bell 20, bolted to a housing 2lfor the horn-driving elements, the housing being in turn secured to acase 22. The latter encloses an electric motor unit 23, havingassociated program cams and contacts as hereinafter described, and alsoencloses fuses and a relay 24 for operating the horn. Certain adjustableelements of the horn proper, generally designated 25, may be disposedwithin the casing 22, and the face of the latter shown in Fig, 1 mayconveniently comprise a door or cover plate hinged (at 26a) to open uponrelease of the toggle bolts 26, for access to the enclosed parts,including the elements 25. For convenience of access and adjustment theparts generally designated 23 and 24 are mounted on the inside of thedoor and are swung out of the casing with it. It will be understood thatparticularly where the apparatus is to be used at sea or off shore, ason a floating buoy, or where it is otherwise to be exposed to weather ormoisture, the entire assembly of casing 22, housing 2| and the inner end2l of bell 20, must be thoroughly water-tight. To that end, theperipheries of diaphragms, interposed gaskets, and other joinedelements, may be embedded in waterproof plastic material, such asglyptol lacquer. A coneshaped or other deflector a may be disposed belowthe mouth of bell 29, and may be vertically adjusted on its supportingbolts to permit some change of the resonant length of the air column inthe bell or trumpet.

Referring now to Figs. 2 to 4 inclusive, there is supported within thehousing 2| an electromagnet generally designated 3|), and comprising alaminated iron or preferably laminated steel core, having a central pole3| and flux-returning portions 32 terminating in the same plane as thepole 3|, to provide adjacent pole elements of opposite polarity, forpowerful signal action; the magnet winding 33 is conveniently disposedabout the central pole member 3|, as shown. The central portion of theiield core, viz. the pole member 3|, is conveniently provided with alongitudinal hole or tunnel, to admit a tubular shaft or connectingmember 34 which is part of the vibrating assembly hereinafter described.The hole or tunnel is conveniently lined with a copper tube 34a, pressedin place, to prevent displacement of the laminations of the member 3|and to guard against an accumulation of rust in the hole, which mightotherwise interfere with free movement of member 34.

The diaphragm structure of the horn advantageously comprises a pluralityof relatively thin diaphragms disposed in parallel and preferablyarranged so that the distance between the diaphragms at the respectiveends of the entire set is of substantial extent. For example, in theconstruction shown, there are provided two groups of diaphragms 35, 36,separated by a substantial space; the inner diaphragm group 35conveniently comprises three diaphragms 35a spaced slightly apart, whilethe group 36 comprises two diaphragms 36a, likewise spaced slightlyapart. The diaphragms are peripherally retained to the housing 2| by aplurality of bolts 3l, circumferentially spaced around the assembly.Thin supporting rings 38 serve to space the diaphragms within therespective groups, and the groups are separated by a cylindrical spacingmember 39, and all parts are preliminarily retained in place by thebolts 3l and securely clamped to the housing' 2| by a plurality of bolts40 spacedvaround and passing through a flange on the bell or trumpet J,whereby the latter is also clamped against the diaphragm assembly andhousing 2|. It will be noted that the annular face of the bell whichabuts against the diaphragm assembly, specifically the outer diaphragmgroup 36, is provided with a relatively wide annular groove 4|, so thatthe area of contact between the bell or horn proper, and the diaphragmassembly, is confined to a pair of spaced, concentric and relativelynarrow annular paths 42, 43, affording an extremely close iit of thebell 20 against the diaphragm assembly and the housmg.

The several diaphragms 35a, 36a are centrally pierced by and secured toa sleeve 45, having its interior in threaded engagement with the oui-,-side of tube 34. Intermediate the several diaphragms of each group onthe sleeve 45, central spacing washers a are provided for accuratelyspacing the diaphragms at the center, and when the assembly is made up,the ends of the tube 45 are advantageously upset or riveted against theheavy terminal washers 45h, whereby each diaphragm group is firmlysecured against its corresponding shoulder 45o on the tube 45. Theopposite end of the tube 34 on the other side of the electro-magnet 3|),is seated in an armature 46, which comprises laminations of iron orpreferably steel in the same plane as laminations of the field core 3|,32, and which is disposed in proximity to the poles of the latter. Along bolt 4l extends through the tubular` shaft 34 into threadedengagement with a member 43, which provides an extension for the shaft34 beyond the armature 45, and into which the bolt 41 may be tightenedso that the head of the latter engages a lock washer 49a against a largeknurled washer sie which is keyed to and abuts the end of sleeve 45, andthe sleeve is locked in adjusted position on the shaft 34. Before thebolt 4l is tightened, the knurled washer 49 may be turned to screw thesleeve 34 longitudinally in the sleeve ll so as to adjust the air gapbetween armature 45 and the core lil-32.

It will be understood that in the preferred construction shown, thepassage of shaft 34 through the hole in pole 3| (strictly speaking,through the tube 34a) is completely free,-i. e., there is no contactanywhere,-and indeed the shaft is entirely clear of supportingengagement or abutment at any point above the diaphragm assem bly asseen in Fig. 2. That is, the spaced groups of diaphragms 35, 35, servealone, and very satisfactorily, to support the remainder of thevibrating assembly, including shaft 34 and the driving armature 46.Frictional, spring or other supplementary supports for the vibratinginstrumentalities are thus entirely eliminated, and at the same time thearrangement is such that the respective positions of the various partscarried by or connected to the shaft 34 may be readily adjusted and theparts accurately locked in adjusted position. Furthermore, by virtue ofthe inclusion of a plurality, and preferably a multiplicity, of spacedparallel diaphragms which are each relatively thin, an eminentlydesirable stiffness is obtained for the diaphragm structure withouttendency of breakage on the part of its individual constituents. Inother words, the diaphragm arrangement may safely be stiff enough toprovide a desirably high pitch, although a relatively heavy armature 4Bis used to obtain powerful driving action. For example, a horn of thetype shown has been satisfactorily constructed to produce a note of 205to 210 cycles per second, yet strong enough to be heard clearly forseveral miles, under average listening conditions.

The outer end of the member 48 carries one contact 50a of a pair ofcontacts generally designated 5G, and arranged to open or close inaccordance with longitudinal displacement of the shaft 34. The othercontact 50o of the set is mounted on a spring 5|, conveniently securedto but insulated from the casing 22. To avoid exing of its end portion,the spring 5| may have a reinforcing plate, or it may preferably haveintegral upwardly turned ears 52 along its sides, which not onlyreinforce the end of the spring, but enlarge its end area so as toprevent breakage adjacent the hole where contact 50h is mounted. Thecontact 5017, moreover, preferably has a tubular shank 50c whereby it isriveted in the hole of the spring, so that when the contact heats up inuse, the shank may expand inwardly and avoid straining the spring Theouter end of the spring 5| extends beyond the contacts and is adapted tostrike an anvil member 53 which is thus arranged to limit the motion ofthe spring downward as seen in Fig. 2. The anvil member 53advantageously comprises a worm wheel mounted on a shaft which isthreaded into a cross member 54 that is suitably insulated from thehousing 2| and case 22 (it being understood that the housing and caseare conveniently bolted together at 55a, as shown). The lower end of theworm wheel shaft has threaded on it a leaf spring 53a, which has itsends abutting the under side` of the member 54 and which strongly biasesthe worm gear in a downward direction to prevent play and chatter. A pin53h, carried by member 54, engages a slot in the leaf spring 53a toprevent rotation of the latter.

A worm 55 is journaled in suitable supports on the member 54, forrotative engagement with the wheel 53, and is provided with a milled ortoothed wheel 56, and an operating shaft 51 having a slotted head. Acheck spring 58 releasably engages the teeth of the wheel 56; and thearrangement is such that by inserting a screw driver in the slot ofmember 51, and turning the same, the Y worm 55 will rotate the gear 53and raise or lower the upper or anvil face of the latter with respect tothe outer end of spring 5|. During such adjustment the check 58 clicksover the teeth of wheel 55, but serves to lock the assembly in anyadjusted position. The slotted shaft or head 51 is preferably insulatedfrom the assembly of wheel 58 and worm 55, so as to prevent electricshock to the operator making adjustments, or inadvertent groundingshould his screw driver also touch the metal casing. Preferably both theanvil 53 and contact spring 5| are of hardened steel construction, formaximum wear resistance. It will now be explained that the partsgenerally designated 25 in Fig. 1 may comprise the elements 51-55-53-5I-50, which are thus readily accessible, through the door ofcasing 22, for inspection and adjustment.

It will be understood that the lower contact 5to may be mounted forvertical adjustment in f' member 48, as by a shank threaded into thelatter and carrying a lock nut 48a, so that the contact may be locked inposition of best alignment with Contact 58h.

The instrumentalities hereinabove described are also diagrammaticallyshown at the upper part of Fig. 5, except that for purposes of sim-vplicity the diaphragm structure is shown as a single diaphragm member6U. It will here be seen that the internal wiring arrangement of thehorn is simply such that the Winding 38 is connected in series with thecontacts 50 across the input terminals 5|, the path from the contacts 50to the lower one of the terminals 6| being conveniently through groundas diagrammatically indicated. Actually, in the apparatus of Figs. l to4, this grounded path extends from contact 5ta through the shaft 34 andthe diaphragm assembly, to housing 2|. l

VAssume for the time being that a suitable source of current, such as astorage battery, is connected across the terminals 5|. Contacts 50 arenormally in closed position, and the winding being thus energized, thearmature 46 is attracted by the field poles 3|, 32. The contacts remainclosed, i. e., the spring 5| follows the downward displacement of thearmature 4E (Fig. 5), until the outer end of the spring strikes theanvil 53. The downward stroke of the .armature and diaphragm assembly46--60 then continues, as will now be well understood, and upon thereturn stroke (initiated by the energy stored in the diaphragm),contacts 50 again close, and under a presently preferred adjustment withrespect to the natural period of the vibrating system, the spring 5| isflexed back to and past its original position as shown in Fig. 5, andthe cycle is repeated. Other things being equal (except the currentconsumption) the amplitude of diaphragm vibration is dependent upon thespace E2 intermediate the upper surface of anvil 53 and the outer end ofspring 5| in its neutral or rest position; that is. the wider the spacethe longer the contacts 5f! are closed during each stroke, and thegreater the force exerted on the armature 46. It will now be seen thatthe described horn structure, including the worm 55 for varying theposition of anvil member 53 with respect to the spring 5|, is providedwith effective means for adjusting the amplitude of diaphragm vibration,so as to obtain and maintain the desired amplitude at all times andwithout excess current consumption.

When the horn is used for marine signalling purposes, for which it isnotably adapted, it must draw a relatively substantial current in orderto produce a signal sufciently powerful to be heard, say, for severalmiles. Under such circumstances-for example, where the horn is locatedand hooked up, as on a floating buoy, to operate automatically atfrequent intervals-long continued use is apt to wear down the surfacesof the rapidly operated contacts 55 (even though a condenser 63 or acondenser-resistor unit is connected across them, as shown in Fig. 5),or more particularly to carry metal from one contact to the other, thuscausing the pitting of one contact and the building up of the othercontact so as to disturb their parallelism and their relative positionsin operation. Fig. 5 accordingly shows a particularly advantageousarrangement for automatic intermittent operation of the horn, and at thesame time, for avoiding or greatly reducing the wear on the contacts.

It has been explained hereinabove that the casing 22 may contain a motor23, together with an associated cycling mechanism and a horn controllingrelay 24. As shown diagrammatically in Fig. 5, the electric motor 23,which may be energized from a pair of storage batteries 65, 6B,connected in series, is adapted to drive a pair of cams 61, 68. Althoughother` motors may be satisfactorily employed in many cases, I prefer touse a motor of the type described and claimed in United States PatentNo. 1,985,357, to Charles F. Wallace, for Electric motor apparatus; itwill be understood that where the device is expected to operatecontinuously for long periods of time and without attention, it isdesirable to employ a motor having the low current consumption, constantspeed and general dependability characteristie of the patented motor.

Cam E1 is provided, for example, with two oppositely disposed risesorhigh spots 69, and a pair of normally open cam contacts 10 are arrangedto be closed by each passage of a rise ES--thus in the instance shown,twice during each revolution of cam 6l. Cam '68, which may be assumed torotate at the same speed as cam 6l, is provided with a single rise 1I,which is longer in extent than either rise 69 of cam El, and which is sodisposed that it shifts a contact-operating follower 'l2 shortly beforecontacts ll are closed by one rise @Q of cam l, and keeps the followerin shifted position until after the same rise @Si (on cam 6l) has passedthe contacts l@ and permitted them to reopen. When shifted, the followerl2 is adapted to open the normally closed contacts 'I3 and to close thenormally open contacts 14.

One of the input terminals 5l of the horn is connected through conductorl5 to the connection T6 between the batteries li and E55; the otherinput terminal of the horn is connected through conductor 16a, heavyduty contacts 'll (normally open) of the relay 24, to the common contactmember 12a of the contacts i3, la. The other sides of the contacts i3,lll, are respectively connected to the opposite ends of the batteries65, ES, and it will now be appreciated that, assuming contacts ll to beclosed, the horn is connected to battery 65 or battery 6% respectivelyaccordingto Whether contacts 'i3 or 'I4 are closed. Furthermore, sincethe sides of the batteries G5 which are connected together through thecommon connection l5 are opposite in sign, the current flow through thehorn when contacts 'i3 are closed is in the reverse direction from thei'low when contacts 'i4 are closed. The low-current relay 2t isconveniently used to avoid the association of heavy duty contacts withthe timing cam 6l (although in some cases heavy duty contacts may beused at 'lll and the relay 2t omitted), and the winding of the relay maybe connected, as shown, through contacts 'lil to the midpoint 'i6 of thebatteries, and also through the contact arm 12a and selectively throughcontacts 'I3 or 14, to the other side of one or the other of thebatteries in the same manner as the horn itself.

Assume now that the motor 23 is rotating the cams 6l, S3 in acounterclcckwise direction, from the position shown in Fig. 5. The rise'si of cam 5'! rst shifts the follower` 'l2 so as to close oontacts 'i4and open contacts 'lf-.3. Thereafter one rise 69 of cam 6l causescontacts lil to close and the relay 24 is accordingly energized frombattery 65. Energization of relay 2li closes its contacts ll, so thatcurrent is supplied to the horn, through its input terminals El, frombattery S55-contacts 'lil being now closed. The horn continues to blowuntil the rise i:3S passes contacts 1G, opening them, therebyde-energizing relay 213 and opening its contacts 'Il in the supplycircuit to the horn. Thereafter, the follower '.'2 drops down from therise H, and contacts 'i3 are closed. They remain closed during the timethat the other or opposite rise Eil or cam Eil closes the contacts lil;and it will now be understood that when the contacts 'lll are thus againclosed to energize the relay 2d and operate the horn, both the relay andthe horn are supplied from battery 65, and current flows through thehorn in the reverse direction from that during the immediately previousperiod of energization. In other words, as the motor 23 continues todrive cams 5'! and 68, the horn is periodically sounded and thedirection of current flow through it is reversed each time, so that wearor other disturbance of the horn contacts 53, particularly as occasionedby transposition of metal between these contacts, is very greatlyreduced; the action at the contacts 50 is thus, so to speak, a series ofbrief tendencies to carry the metal rst one way and then back againrespectively, so that over a longr period of time the contacts arerelatively unai'lected by metal transposition.

It will be noted that the arrangement of cams El and B8 is such thatcontacts 'E3 and 'M are operated at times when no current is owing, soas to avoid wear of these contacts by arcing. At the same time, it willbe noted that the program contacts 'ill and the heavy duty relaycontacts 'll both benefit by the same reversal of current flow which isprovided for the horn; in conseduence, wear or other deformation ofcontacts 'le and ll is greatly obviated.

It will be appreciated, ol course, that the number of rises Si) o-n camEl and correspondingly the use of one or more rises H on cam 68 may bevaried to suit requirements oi design or operation. In one embodiment ofthe invention, the arrangement has been that shown in 5, with the rises69 of such length, and with the motor 23 driving the cam 67 at such rate(2 R. P. l\/I.), that the horn makes four one-second blasts each minute;and with continuous operation of that character for a period exceedingsix monthsfour blasts per minute, day and night-there was no appreciabledeformation of the contacts 59 and very little appreciable wear.

It will be understood that the capacity of condenser G3 (for ease inmounting, two condensers 53 are shown in Fig. 3 and will be understoodconnected in parallel) may be readily selected to coordinate the periodof the electrical circuit with the natural period of the mechanicalelements.

It will now be appreciated that the present invention not only affords ahorn which is relatively simple in construction, dependable inoperation, and easily built, to have any predetermined pitch within awide range, but also ailoids distinctively improved control arrangementsfor such horns so as to avoid contact wear and impairment of normaloperation. The advantages realized by the invention are, furthermore, ofspecial importance where the signal device is to be automaticallyintermittently operated at freo uent intervals and in a location as on amarine buoy) where it must give reliable service without frequentattention. On the one hand, the working vibration of the diaphragm andassociated driving assembly is necessarily powerful, and tends to set updisturbing vibrations in every part that is mechanically connected withthe apparatus; on the other hand, the electrical parts, notablycontacts, are subjected to driving or control operation on each of themany hundred or often several thousand separate occasions on which thesignal is operated every day. The invention is particularly eiective inobviating or minimizing the wear or other derangement which wouldotherwise inevitably result from the strenuous operating conditions justdescribed.

In accordance with the provisions ol the patent statutes, I have hereindescribed the principle of operation of my invention, together with theapparatus which I now consider to represent the best embodimentsthereof, but I desire to have it understood that the apparatus disclosedis only illustrative and that the invention can be carried out by othermeans. Also, while it is designed to use the various features andelements in the combinations and relations described, some of these maybe altered and others omitted and some of the features of eachmodification may be embodied in the others without interfering with themore general results outlined, and the invention extends to such usewithin the scope of' the appended claims.

I claim:

l. Sound signal apparatus comprising, in combination, an electromagnet,an armature therefor, make-and-break contacts in series with theelectromagnet and associated with said armature for causing Vibration ofthe latter toward and away from the electromagnet, one of said contactsbeing carried with the armature and the other contact having asupporting spring for maintaining the contacts closed during asubstantial part of each cycle of vibration, a supporting memberconnected to the armature, and a stili diaphragm assembly comprising aplurality of peripherally mounted, spaced diaphragms centrally securedto said member for drive by the armature and arranged in a plurality ofsets Widely spaced apart at all points to provide the sole support forsaid member, armature and firstmentioned contact, said apparatusincluding means peripherally mounting the diaphragms in the aforesaidspaced relation, and said mounting means comprising means rigidlyclamping the diaphragms about their peripheries.

2. In sound signal apparatus, in combination, a plurality of sets ofrelatively closely spaced, thin, peripherally mounted diaphragmscentrally pierced by and secured to a connecting member therefor, anarmature spaced from said diaphragms and mounted on an extended portionof said connecting member, said sets of diaphragms being substantiallywidely spaced and providing the sole support for said connecting memberand armature, electromagnetic means associated with the armature foreffecting vibration of the diaphragms in unison, supporting structurefor the apparatus, and mounting means for the diaphragms, rigidlyperipherally clamping said diaphragms to said supporting structure inthe aforesaid spaced relations of the diaphragms and sets thereof.

3. In an electric horn, the combination with an electrically vibrateddriving element, of a soundproducing assembly adapted for prolongedvibration at a frequency of not less than about 200 cycles and at anamplitude for normal audibility of not less than a mile, and comprisingat least several peripherally secured, thin, centrally interconnecteddiaphragms spaced apart at all points and including two substantiallywidely spaced diaphragms, all of said diaphragms being disposed togetheron one side of said driving element and connected to said element to bedriven thereby, said horn having a supporting structure and saiddiaphragms having associated securing means for rigidly peripherallyclamping said diaphragms to the supporting structure in the aforesaidspaced relation, and said diaphragms having lll individual nexibllityand combined stiffness cooperating to provide the aforesaidcharacteristics of frequency and amplitude of vibration of the soundproducing assembly.

4. Electric warning signal apparatus comprising, in combination, a stiffsound-producing diaphragm structure comprising at least severalperipherally mounted, thin diaphragm spaced apart at all points andcentrally interconnected for vibration in unison, and electrical drivingmeans therefor including an electromagnet having a massive armature tobe vibrated thereby, for development of substantial driving power, tovibrate the diaphragm structure at a predetermined desired frequency,said electromagnet being disposed intermediate said diaphragms and saidarmature, said armature being thereby spaced substantially from saiddiaphragms and said armature 'being mechanically connected to saiddiaphragms centrally of the latter for drive of and support only by saiddiaphragms, said diaphragms being spaced and including two which arewidely spaced apart, and said diaphragm structure being thereby adaptedto support said massive armature for vibration by and with the armatureto provide a signal of large amplitude at the desired frequency; saidapparatus including mounting means rigidly peripherally clamping saiddiaphragms in the aforesaid spaced relation.

5. An electric horn comprising, in combination, a relatively stiffsound-producing assembly adapted for prolonged vibration at apredetermined desired frequency and at high amplitude for distantaudibility and comprising a plurality of sets of spaced, peripherallymounted, thin diaphragms, said sets of diaphragms being widely spacedapart and all of said diaphragms being centrally interconnected tovibrate in unison, and electrically operated driving means for effectingvibration of said assembly at said desired frequency, said hornincluding mounting means rigidly peripherally securing said diaphragmsin said spaced relation.

6. In an electric horn to be operated on direct current, the combinationwith electrical driving means comprising an electromagnet, an armaturetherefor and associated make-and-break contacts for eecting vibration ofthe armature, of a diaphragm structure to be driven by said armature andadapted to cooperate with the armature to provide a self-excitedassembly vibrating at desirably high amplitude and comprising aplurality of peripherally secured diaphragms appreciably spaced apart atall points and disposed together at one side of said driving means, andmeans fastened centrally to said diaphragms for connecting same to thearmature,

. said horn having a supporting structure and said cliaphragms havingassociated securing means for rigidly peripherally clamping saiddiaphragms to the supporting structure in the aforesaid spaced relation.

JOHN R. MAcKAY.

